Answers to Your Concrete Questions #1

Q. I have rust stains on the concrete in my basement. What is the best way to remove these stains?

A. One treatment that meets with a fair degree of success is oxalic acid. Sometimes referred as wood bleach, a powder mixed in warm water until it will no longer dissolve in the water. Brush it on the stain, let sit for a few minutes, then rinse thoroughly. Repeat as needed. The powder is an irritant to the eyes and skin. Take care to prevent the powder from getting into the eyes or onto mucous membranes, such as the mouth and nose.

Treatment that is more potent is Muriatic acid. This cleaner is quite hazardous to use, requiring a fair degree of protective clothing for the user and caring for surrounding areas and things to prevent damage from the acid. Of course, the best treatment is to prevent the stains in the first place by protecting the concrete from staining by sealing the concrete or confining the rusting item.

Q. Does anyone know how to neutralize salt once it had been put onto a concrete floor?

A. The simplest approach would be to hose it off. Water readily dissolves salt. Sealing the surface when conditions are right will help protect the concrete from this in the future.

Q. I'll be installing a safe in my vacation home for renters to use. It will sit on a shelf and will be attached from behind to a concrete wall. What is the best and most secure method of attachment?

A. If it's solid concrete, then use inserts (like used for drywall). If it's block, you can use toggle bolts, or backing plates.

Q. I recently obtained a chocolate lab pup, and for this reason I need to fence in what isn't fenced in already. I only need a 5x17 rectangle done, however we wanted a deck and new walkway in the same area. The cost for the 5x17 was $220 (1.04 yds) and the cost for all $336. Go figure. My questions are, do I need to put expansion joints between the deck/walkway and deck and 5x17 run? Do I tie into the slab of the house or just butt up against it? Do I need to put some type of barrier between the two slabs (to fight termites etc.)? I want to stamp and stain the concrete also, is this a job that I can tackle and is it going to be expensive? The total I would like to spend is around $600-$700. How many stamps do I need to purchase? The round stays very saturated when it rains more than a day and I have two gutter downspouts where the new deck will be going. Any ideas?

A. You'll need expansion joints about 10 - 12 feet to divide a piece. They actually allow the concrete a designated place to crack without showing overmuch. Stamping is a bit out of the realm of a do-it-yourself project because so much has to be done so fast before the concrete starts to set. For some perspective, you might talk to a couple of companies that stamp concrete to get a rundown on prices and timing for the work. When my shop slab was poured, the crew was churning right along just to finish it smooth before it was starting to set. I can imagine that more help would have been needed to stamp it, too. Staining seems to be reported as more satisfactory if the stain is added to the mix rather than added to the concrete after pouring. Your local redi-mix folks can advise you on how their approach works.

Q. One of my front porch steps has cracked, and I am wondering what I should do so that it does not get any worse. The step slabs are about 2" thick and are some sort of stone. I had new railings installed about a year ago and the crack is where the hole was drilled for the bottom post.

A. You can buy an electrometric caulking material at home improvement stores that is intended for filling joints and holes in concrete and stone. Clean the hole as much as you can, then apply this to fill and seal the hole.

Q. I'm installing a gas fireplace and I'll be adding fieldstone just for looks later on down the road. I was wondering if I could just build the wall on the 6" basement slab or will the floor start cracking?

A. Looking at some rough numbers, the wall will load about 250 pounds per square foot. Most recommendations for this load would indicate a slab of 12 inches. This is starting to appear to be a question for a structural engineer. You certainly don't want the slab to fail later. You can get a lot of reliable information from a structural engineer for a couple of hundred dollars.

Q. I'm removing a door in a concrete block wall and replacing it with a larger door. I need to remove about a foot of the concrete block for the new door. Should I cut it out with some type of saw or grinder, or should I chisel it out?

A. Go to a rental center and ask them to rent you the proper saw: a gas powered diamond blade with an attachment to add water to the blade to keep down dust. A hammer and chisel is a crude way of doing this and you may weaken the structure, and your rough in wood would be hard to fit against a chiseled edge. Before going to the rental center, get some estimates for having this done. The blades are expensive. Break one and you've more than paid to have it done. The chance for breaking a blade is good for a DIYer with little or no experience.

If there are blocks presently over top of the opening, and you make the door wider, make sure that what ever is holding those blocks in place will still be there after you cut your hole bigger. You may have to re-do the support over the door unless there is nothing over it now, in which case, you should be OK.

Q. Having just removed a concrete set of steps on the front of the house, a small section of sill about two feet is rotted about 1/2 way through. The joists are resting on top of a 2x8, which then rests on the 2x4 sill. A portion of the 2x8 is punky as well. How to best remedy this?

A. Perhaps you ought to support the floor from the crawlspace with some 6x6 oak posts held up sideways on jacks to relieve the weight on the damaged portion of the sill plate. Once the weight is off, cut out the damaged wood and replace it. Make sure you ask about what type of wood to use, get structural lumber. Once the damage is fixed, side it to keep it dry.

Q. Any suggestions for cleaning a concrete stoop (two step)? I removed an Astroturf cover installed by the previous owner and there is some sort of adhesive or rubber residue stuck to the concrete.

A. Try to remove any gross residue with a wire brush. Next, try some mineral spirits on a spot to see if that will remove it. Next, try lacquer thinner in a spot. Unless you know what the adhesive is, it will be trial and error finding a solvent.

Visit our Community Forums for more answers to your home improvement questions.